Grey glass composition for production of windows

ABSTRACT

The subject of the invention is a gray glass composition of the soda-lime-silicate type having an overall light transmission under illuminant A (T LA ) greater than 67% for a glass thickness equal to 3.85 mm, which comprises the constituents below within the following limits by weight: 
                                       SiO 2     64–75%         Al 2 O 3      0–5%         B 2 O 3      0–5%         CaO    5–15%         MgO    0–5%         Na 2 O   10–18%         K 2 O    0–5%                                     
and the coloring agents below within the following limits by weight:
 
     
       
         
               
               
               
             
                   
                   
               
                   
                 Fe 2 O 3   
                 0.25–0.65% and preferably 0.5–0.65% 
               
                   
                 CoO 
                 less than 20 ppm, preferably less than or 
               
                   
                   
                 equal to 15 ppm 
               
                   
                 NiO 
                 40–250 ppm and preferably 70–150 ppm 
               
                   
                 Se 
                 0–5 ppm 
               
                   
                   
               
                   
                 where Fe 2 O 3  is the total iron.

The invention relates to a glass composition of the soda-lime-silicatetype intended for the production of flat glass of gray tint. Althoughthe invention is not limited to such an application, it will be moreparticularly described with reference to automobile applications,especially for forming windshields and side windows located at the frontof a vehicle.

Windows intended for the automobile industry are subject to requirementsof various kinds. With regard to optical properties, these requirementsare governed by regulations, for example in the case of the lighttransmission of a windshield, or else governed by concern for thecomfort of the user, for example as regards energy transmission, or elsefor esthetic reasons, especially as regards color.

Apart from the requirements relating to light transmission and to energytransmission, the windows located at the front of vehicles must satisfythe esthetic desires of automobile manufacturers as regards color, inparticular relative to the dominant wavelength and to purity.

Although coloring agents typical of giving such or such a color aregenerally known, it is difficult to find a particular color in terms ofwavelength and purity, combined with specific characteristics, forexample light transmission and energy transmission factors within awell-defined range of values.

Thus to obtain a gray glass, it is known to add coloring agents to thebatch materials intended to be melted in order to produce the glassmatrix. These coloring agents are, for example iron, selenium, nickel,cobalt, cerium, or erbium, etc.

Some of these agents, such as erbium, are expensive and for this reasonare not employed or are added to the glass composition only in a verysmall amount.

Others are deemed to be highly polluting and require the fitting ofsubstantial filtration systems, which generates a high cost burden. Thisis especially the case with selenium, which is commonly employed forproducing gray glass, but 70 to 85% by weight of it is released into theatmosphere when it is melted. Consequently, the filtration systemsspecific to this element, with which melting plants are fitted so as toprevent pollution of the atmosphere, increase the production cost ofsuch glass. Moreover, such glass is difficult to process becauseselenium has several oxidation states.

Yet other coloring agents allow the desired color to be obtained only iftheir content in the glass composition is relatively high. Introducing alarge amount of colorant containing nickel into the glass compositionresults in the formation of nickel sulfide beads within the glass.Window panes produced from such glass have a tendency to fracture whenthey are subjected thereafter to a thermal toughening treatment becauseof the presence of these beads.

It is already known to produce gray-colored glass using a glasscomposition containing iron oxide, cobalt oxide and selenium. Such glassis, however, very dark and consequently does not meet the conditionsrequired for front windows of a vehicle.

Compositions have been proposed in EP-A-0 653 386 for obtaining grayglass that can be used for automobiles. These compositions arecharacterized in that they contain either a mixture of iron oxide,cobalt oxide and selenium, or a mixture of iron oxide, cobalt oxide andnickel oxide, and possibly selenium. The compositions comprising nickeloxide contain cobalt oxide in an amount at least equal to 20 ppm. Suchglass obtained from compositions of the latter category has a lighttransmission factor (TL_(A)) ranging from about 60% to about 72%, whichmeets the conditions required for use as a windshield and/or a frontside window. However, windows having a TL_(A) factor equal to or greaterthan 70% do not have a high energy transmission factor (T_(E)), thisbeing at best equal to about 58%.

The object of the present invention is to propose a gray glasscomposition of the soda-lime-silicate type that has an overall lighttransmission under illuminant A (T_(LA)) compatible with use as a frontwindow of an automobile, in particular a windshield, and a satisfactoryoverall energy transmission, and which can be sheeted on a bath of metalusing the float glass technique.

The subject of the present invention is a glass composition that allowsa window having a relatively neutral gray coloration to be obtained.

The subject of the present invention is also a glass composition thatcan be produced under the oxidation-reduction conditions usuallyobserved for a standard float glass, and the cost of which is close tothe cost of the latter.

These objects are achieved according to the invention thanks to a grayglass composition of the soda-lime-silicate type having an overall lighttransmission under illuminant A (T_(LA)) greater than 67% for a glassthickness equal to 3.85 mm, which comprises the constituents belowwithin the following limits by weight:

SiO₂ 64–75%  Al₂O₃ 0–5% B₂O₃ 0–5% CaO 5–15%  MgO 0–5% Na₂O 10–18%  K₂O0–5%and the coloring agents below within the following limits by weight:

Fe₂O₃ 0.25–0.65% and preferably 0.5–0.65% CoO less than 20 ppm,preferably less than or equal to 15 ppm and better still 5–15 ppm NiO40–250 ppm and preferably 70–150 ppm Se 0–5 ppm where Fe₂O₃ is the totaliron.

According to a preferred embodiment of the invention, the overall energytransmission (T_(E)) is less than or equal to 55%, preferably less than50%, for a thickness of 3.85 mm. Such requirements correspond inparticular to those required in the automobile field in order to providefor the thermal comfort of passengers in the passenger compartment. Alsopreferably, the glass composition has a dominant wavelength underilluminant D₆₅ of between 480 and 550 nm, preferably between 490 and 510nm, and an excitation purity under the same illuminant of less than 6%,preferably less than 5%, for a thickness of 3.85 mm. Such requirementscorrespond in particular to those required for the desired neutralcoloration in the case of front side windows of automobiles. The glassobtained may have a tint ranging from gray-blue to gray-green dependingon the dominant wavelength.

Also preferably, the glass composition has a redox value of less than0.55 and preferably less than 0.35, and better still greater than 0.18.The redox value is defined by the ratio of the FeO content to the totaliron content, expressed in Fe₂O₃ form, the contents being expressed aspercentages by weight.

According to an advantageous embodiment of the invention, thecomposition contains no intentionally added selenium, except for theimpurities that may be introduced by certain raw materials.

According to another particularly advantageous embodiment of theinvention, and especially for applications of the windshield and sidewindow type for automobiles, the overall light transmission underilluminant A (T_(LA)) is greater than or equal to 69%, preferablygreater than or equal to 70%, and the energy transmission is less than50%, preferably less than 48%, for a thickness of 3.85 mm.

In the glass according to the invention, the silica is generallymaintained within very narrow limits for the following reasons: aboveabout 75%, the viscosity of the glass and its ability to devitrifygreatly increase, which makes it more difficult for the glass to meltand to flow on a bath of molten tin, while below 64% the hydrolyticresistance of the glass rapidly decreases.

This reduction in the hydrolytic resistance of the glass may becompensated for, at least in part, by the introduction of Al₂O₃, butthis oxide contributes to increasing its viscosity and reducing thetransmission in the visible. Consequently, it is envisioned to use itonly in a very small amount.

The alkali metal oxides Na₂O and K₂O facilitate melting of the glass.K₂O may be used up to about 5%, since above this the problem of the highcost of the composition arises. The sum of the Na₂O and K₂O contents,expressed as percentages by weight, is preferably equal to or greaterthan 13%.

Alkaline-earth metal oxides play a key role in obtaining the propertiesof the glass according to the invention.

As regards the oxide MgO, according to a first embodiment of theinvention, its content is advantageously greater than 2%, especially foreconomic reasons.

According to another embodiment, its content is less than 2%. This isbecause it has been demonstrated that limiting the MgO content to 2% hasthe effect of shifting the maximum in the FeO absorption band towardlonger wavelengths, thus making it possible to increase the infraredabsorbtivity without impairing the transmission in the visible. Completeelimination of MgO, which plays an important role in the viscosity, maybe compensated for, at least in part, by increasing the content of Na₂Oand/or SiO₂.

BaO makes it possible to increase the light transmission, and it may beadded to the composition according to the invention with a content ofless than 4%. This is because BaO has a much smaller effect than MgO andCaO on the viscosity of the glass. Within the context of the invention,the increase in BaO takes place essentially to the detriment of thealkali metal oxides, MgO and especially CaO. Any significant increase inBaO therefore contributes to increasing the viscosity of the glass,especially at low temperatures. In addition, introducing a highpercentage of BaO substantially increases the cost of the composition.Preferably, the glass according to the invention contains no BaO. Whenit does contain BaO, its content is preferably between 0.5 and 3.5% byweight.

Apart from complying with the limits defined above for the variation inthe content of each alkaline-earth metal oxide, it is preferable inorder to obtain the desired transmission properties to limit the sum ofthe percentages of MgO, CaO and BaO by weight to a value equal to orless than 14%.

When it is desired to produce selective glasses (that is to say glassescapable of absorbing radiation within a desired wavelength range, forexample corresponding to ultraviolet or infrared radiation, withoutappreciably affecting the light transmission), the glass compositionsmay furthermore include at least one optical absorption agent, such asCeO₂, TiO₂, Cr₂O₃, V₂O₅, WO₃, La₂O3, etc. The total content of this(these) agent(s) is generally maintained at less than 2% by weight ofthe composition, and preferably less than 1%.

The glass according to the invention may also contain up to 1% of otherconstituents provided by the impurities in the glass raw materialsand/or by introducing recycled cullet into the glass batch and/or byusing a refining agent (SO₃, Cl, Sb₂O₃, As₂O₃).

To facilitate melting, and especially to make this mechanically useful,the matrix advantageously has a temperature, corresponding to aviscosity η such that log η=2, which is less than 1500° C. Morepreferably, especially when it is desired to obtain the glass in theform of a glass ribbon using the float glass technique, the matrix has atemperature corresponding to the viscosity η, expressed in poise, suchthat log η=3.5 (denoted by T_(log η=3.5)) and a liquidus temperature(denoted by T_(liq)) which satisfy the equation:T _(log η=3.5) −T _(liq)>20° C.,and preferably the equation:T _(log η=3.5) −T _(liq)>50° C.

A better appreciation of the advantages of the present invention will begained from the examples of glass compositions given below.

In these examples, the values of the following properties, measured fora thickness of 3.85 mm, are indicated:

the overall light transmission factor under illuminant A (T_(LA))between 380 and 780 nm;

the overall energy transmission factor (T_(E)) integrated between 295and 2500 nm according to the ISO 9050 standard (Parry Moon, air mass 2);

the ultraviolet solar radiation transmission factor (T_(UV)) calculatedaccording to the ISO 9050 standard;

the dominant wavelength (λ_(d)) under illuminant D₆₅; and

the excitation purity (P_(D65)) under illuminant D₆₅.

The light transmission (T_(LA)), the dominant wavelength (λ_(d)) and thepurity (P) were calculated using the 1931 CIE (Commission Internationalede l'Eclairage) calorimetric reference observer.

Each of the compositions given in the table was produced from thefollowing glass matrix, the contents of which are expressed aspercentages by weight, each being corrected in terms of silica in orderto be adjusted to the total content of coloring agents added:

SiO₂ 71.00%  Al₂O₃ 0.70% CaO 8.90% MgO 3.80% Na₂O 14.10%  K₂O  0.10%.

The temperatures T_(log η=2) and T_(log η=3.5), corresponding to theviscosities, expressed in poise, such that log η=2 and log η=3.5respectively, together with the liquidus temperature T_(liq) areidentical for all the glass compositions given (these being producedfrom the same glass matrix) and are the following:

T_(logη=2) 1410° C. T_(logη=3.5) 1100° C. T_(liq) 1060° C.

The glasses of examples 1 to 5 are examples produced according to theinvention, the compositions of which were measured, whereas the glassesof examples 6 to 18 are given with their theoretical compositions.

Examples 1 to 18 according to the invention show that, within a widerange of coloring agents, it is possible to obtain neutral gray glassthat meets the optical constraints, namely a high overall lighttransmission (T_(LA)>67%) and a relatively low energy transmission, atmost equal to 55%. These good glass properties result to a large extentfrom the fact that the cobalt oxide content in the composition is lessthan 20 ppm. The examples also show that the target optical propertiescan be achieved without adding selenium, this being particularlyadvantageous as regards costs and the risk of polluting the environment.

Any glass obtained from the compositions according to the invention iscompatible with the usual techniques for manufacturing flat glass. Thethickness of the glass ribbon obtained by sheeting out the molten glasson a bath of tin may be up to 20 mm, and in general this will varybetween 0.8 and 10 mm.

Window glass (obtained by cutting the glass ribbon) may subsequentlyundergo a bending and/or enameling operation, especially when it is usedfor automobile windows.

To produce windshields or side windows, the window glass is initiallycut from a glass ribbon whose thickness generally varies between 3 and 5millimeters. With these thicknesses, the glass ensures good thermalcomfort. The windshields or side windows in question may be laminated,in which case they are formed from several glass sheets, at least one ofwhich is obtained from the composition according to the invention.

The windows falling within the scope of the present invention may besubjected beforehand to surface treatments or may receive, for example,an organic coating, such as a polyurethane-based film withantilacerating properties, or a film that provides sealing should awindow shatter.

These windows may also be coated with at least one metal oxide layerobtained by high-temperature chemical deposition using pyrolysis orchemical vapor deposition (CVD) or vacuum deposition techniques.

TABLE 1 2 3 4 5 6 7 8 9 Fe₂O₃ (%) 0.56 0.57 0.54 0.54 0.58 0.51 0.260.50 0.60 FeO(%) 0.15 0.185 0.21 0.165 0.178 0.18 0.13 0.12 0.21 Redox0.27 0.32 0.39 0.30 0.31 0.35 0.50 0.24 0.35 value CoO (ppm) 9 6 10 9 100 14 13 3 NiO (ppm) 150 100 80 80 80 150 150 200 45 Se (ppm) 0 0 0 0 0 00 0 0 T_(LA)(%) 69.3 70.3 69.0 71.7 70.4 71.7 71.7 69.2 73.2 T_(E)(%)48.9 46.3 44.7 49.4 47.1 48.3 54.9 53.8 46.9 T_(UV)(%) 32.0 32.1 32.133.7 31.2 34.1 51.5 31.0 31.1 λ_(d)(nm) 507 495 493 495 495 507 495 546492 P_(D65)(%) 2.2 4.2 5.4 3.64 4.1 2.3 2.7 3.0 5.7 10 11 12 13 14 15 1617 18 Fe₂O₃ (%) 0.45 0.49 0.34 0.62 0.45 0.51 0.45 0.5 0.45 FeO(%) 0.160.148 0.124 0.13 0.16 0.13 0.16 0.13 0.16 Redox 0.36 0.30 0.36 0.21 0.360.25 0.35 0.26 0.35 value CoO (ppm) 15 14 15 15 10 10 0 19 18 NiO (ppm)50 110 130 80 50 75 143 200 100 Se (ppm) 0 0 0 0 5 0 0 0 0 T_(LA)(%)73.1 71.3 72.1 72.4 69.0 74.5 73.3 67 67.6 T_(E)(%) 51.9 51.9 55.0 54.349.2 55.0 51.4 51.7 49.0 T_(UV)(%) 36.4 33.2 41.7 26.4 30.1 31.1 36.235.0 36.8 λ_(d)(nm) 489 495 496 499 517 497 512 517 494 P_(D65)(%) 5.83.2 2.7 2.6 1.2 2.7 1.8 1.6 3.0

1. A gray glass composition of the soda-lime-silicate type having anoverall light transmission under illuminant A (T_(LA)) greater than 67for a glass thickness equal to 3.85 mm, comprising the constituentsbelow within the following limits by weight: SiO₂ 64–75%  Al₂O₃ 0–5%B₂O₃ 0–5% CaO 5–15%  MgO 0–5% Na₂O 10–18%  K₂O 0–5%

and the coloring agents below within the following limits by weight:Fe₂O₃ 0.25–0.65% CoO less than or equal to 10 ppm NiO 40–250 ppm Se 0–5ppm where Fe₂O₃ is the total iron.


2. The glass composition as claimed in claim 1, wherein the CoO contentis from 5 to 10 ppm.
 3. The glass composition as claimed in claim 1,having an overall energy transmission (TE) of less than 55%, for athickness of 3.85 mm.
 4. The glass composition as claimed in claim 1,having a redox value of less than 0.55.
 5. The glass composition asclaimed in claim 1, wherein the overall light transmission (TLA) isgreater than or equal to
 690. 6. The glass composition as claimed inclaim 5, wherein the overall energy transmission (TE) is less than 48%.7. The glass composition as claimed in claim 1, wherein no selenium ispresent.
 8. The glass composition as claimed in claim 1, having adominant wavelength of between 480 and 550 nm and a purity of less than6% under illuminant D₆₅ and for a thickness of 3.85 mm.
 9. The glasscomposition as claimed in claim 8, wherein the dominant wavelength isbetween 490 and 510 nm.
 10. The glass composition as claimed in claim 8,having a purity of less than 5%.
 11. The glass composition as claimed inclaim 1, further comprising at least one optical absorption agentselected from the group consisting of CeO₂, TiO₂, Cr₂O₃, V₂O₅, WO₃, andLa₂O₃.
 12. The glass composition as claimed in claim 1, wherein thedifference between the temperature corresponding to a viscosity ηexpressed in poise wherein log η=3.5, and the liquidus temperatureT_(liq) is greater than 20° C.
 13. The glass composition as claimed inclaim 1, wherein the temperature corresponding to a viscosity ηexpressed in poise wherein log η=2, is less than 1500° C.
 14. A windowcomprising at least one glass pane whose chemical composition is definedby claim
 1. 15. The window as claimed in claim 14, wherein the pane hasa dominant wavelength of between 480 and 550 nm and a purity of lessthan 6% under illuminant D₆₅ for a thickness of 3.85 mm.
 16. The windowas claimed in claim 15, wherein the pane has a dominant wavelength ofbetween 490 and 510 nm and a purity of less than 5%.
 17. The window asclaimed in claim 14, wherein the pane has a thickness of up to 20 mm.18. A laminated glass window comprising two glass panes, at least one ofwhich is formed from the glass composition as claimed in claim
 5. 19.The glass composition of claim 1, wherein Fe₂O₃ is present in an amountof from 0.5 to 0.65% by weight.
 20. The glass composition of claim 1,wherein NiO is present in an amount of from 70 to 150 ppm.
 21. The glasscomposition of claim 3, wherein the overall energy transmission is lessthan 50%.
 22. The glass composition of claim 4, wherein the redox valueis <0.3.
 23. The glass composition of claim 4, wherein the redox valueis from 0.18 to 0.55.
 24. The glass composition of claim 12, wherein thetemperature difference is >50° C.
 25. The window of claim 17, whereinthe pane has a thickness of from 0.8 to 10 mm.